Health disparities are high among Latinas. They are more likely to be overweight, diagnosed with diabetes, and physically inactive compared to their non-Hispanic White counterparts. Thus, interventions that target improving health access and ameliorating chronic diseases among Latinas are of high public health importance. Available data suggest that community-focused interventions produce improvements in physical activity (PA) and are well-received by Latinas especially when social and physical environments are considered (e.g., social support, safe walking areas, etc.). Research suggests that Latinos respond favorably to technological-based health interventions. Thus, health promotion interventions that can address Latinos? preferences regarding their physical and social environments while utilizing a preferred technology source (e.g., smartphone) could prove highly successful. In a Phase I SBIR, our team developed Caminemos Juntas!, an innovative mobile phone app using Location-based Services (LBS) to connect women within geographically proximal neighborhoods as a way to provide social support for increased walking behaviors. Specifically, we (a) gathered feedback from an Expert Advisory Board (EAB) to help plan and assess the feasibility of creating the app; (b) built connections and gathered input from Latina community leaders to assist in the conceptual development of the app through a Community Advisory Board (CAB); (c) conducted an online survey of a national sample of Latinas on their smartphone usage for health promotion, and interest in social networking and LBS technology features; (d) conducted iterative focus groups with Latinas to guide development of app content, design, and aesthetics to fully develop a functioning prototype; (e) conducted field usability testing with Latinas to test the app?s accuracy to establish users? location and connect users through the Caminemos Juntas! system and users? use and satisfaction with the app; and (f) developed a specifications document to outline the Phase II development plan. The results of the Phase I activities provided strong support for this Phase II SBIR application. The proposed Phase II project will (1) develop a full-scale, fully programmed Caminemos Juntas! app; (2) determine whether the Caminemos Juntas! app can be translated and adapted to a new community environment; (3) test the performance, usage, and usability of the full-scale, fully- programmed app; and (4) evaluate whether Caminemos Juntas! increases physical activity, social support for exercise, and quality of life (QOL) in Latinas. Caminemos Juntas! will be evaluated in a randomized comparative-effectiveness trial (n=200) with Latinas age 18-55 in the Denver, CO and San Jose, CA areas. Overall, the proposed project has the potential to significantly impact Latinas? health by providing them with real-time opportunities to connect socially with the goal of walking. Caminemos Juntas! will be the first app that use geo-location technology dedicated to walking with a social emphasis, for any population.